1. Field of the Invention
This invention relates generally to indicator apparatuses or structures for mounting indicator lights on printed circuit boards. More particularly, it relates to a holder structure for mounting light-emitting diodes (LEDs) on printed circuit boards (PCBs) using “surface mount technology” (SMT).
2. Description of the Prior Art
As is generally known to those skilled in the art, light-emitting diodes (LEDs) are particularly useful as status indicators for various types of electrical circuits and systems, such as in different kinds of proximity sensors for detecting the presence or absence of an object. For example, one or more LEDs may be mounted at a sensor housing so as to provide desired information about the operating condition of the sensor at the housing. The LEDs are very advantageous in this type of operating environment due to the fact that they are small in size and are relatively inexpensive in cost. Further, they consume small amounts of power and have a long useful life.
The LEDs are available commercially from a variety of suppliers which permit direct mounting to a printed circuit board (PCB) via a plurality of eyelets or “through-holes”. However, since the printed circuit board is typically mounted within a chassis of some type the LEDs mounted on the PCB are not usually viewable directly by a user of an electrical system. Heretofore, light pipes consisting of rods or bundles of fibers made of clear plastic or glass have been designed to direct the light from the LEDs to openings formed on, for example, the face or front panel of the electrical system where they may be viewed by the user.
In complex electrical and electronic devices, it is not uncommon that there are used a number of printed circuit boards each having a substantial quantity of circuit components, such as integrated circuit chips, resistors, capacitors, and the like. In view of the advances made in the PCB technology in recent years, the prior art method of mounting the various circuit components on the PCB via eyelets or “through-holes” for making electrical interconnections have been largely replaced by printed circuit boards using “surface mount technology” (SMT). The “wave soldering” technique utilized in the PCBs having “through-holes” is no longer used and have been superceded by radiant or convention heating in an oven for SMT printed circuit boards where the electrical components and their leads are heated so as to cause the pre-applied solder to melt and attach the components to the boards via solder pads.
If the individual LEDs were directly mounted on the SMT printed circuit boards using the “through-holes”, there would be encountered a number of disadvantages associated with this technique. Firstly, the SMT printed circuit board would be required to be modified with such “through-holes” in order to accommodate the individual LEDs. Secondly, after the use of radiant heating for securing the other electrical components to the board another step would be needed to secure the individual LEDs to the board by way of “wave soldering”. These required extra steps are very expensive and would thus increase the manufacturing and assemble cost of the boards.
In addition, even if the individual LEDs could be mounted economically on the SMT printed circuit boards they would be typically required to be elevated above the board so as to be visible to a user. However, the conductive leads usually provided for the individual LEDs tend to be very pliable and narrow so as to be unable to support and accurately locate them very high off the board or near the edge of the board. Therefore, the use of the advanced surface mount technology has created a demand for structures and techniques for mounting and positioning indicator lights, i.e., LEDs, on PCBs using SMT with strength and accuracy.
Accordingly, it would be desirable to provide a holder structure for mounting indicator lights, particularly LEDs, on printed circuit boards using surface mount technology with strength and accuracy. It would be expedient that the holder structure includes a housing being capable of mounting two-high LEDs one disposed above the other for attachment to conductive solder pads on a SMT printed circuit board with a high degree of mechanical strength and precision.